Beginners Guide to Database
Aggregate Functions in Relational Database
Aggregate Function or Aggregation Function in Relational Database is a function which returns a single Summary Value from the values of multiple rows grouped together.
Some of the mostly used Aggregate Functions are discussed below
1. COUNT
Basic Syntax:Here is the Syntax to count all the rows in a Table;
Select COUNT(column name) from Table;
Example:
The following query counts all the rows from tbl_employee whose name column is not empty.
Select COUNT(name) from tbl_employee;
Basic Syntax with condition:
Here is the Syntax to Count total rows in specific condition. WHERE keyword is used to add the condition in query.
Select COUNT(column name) from Table WHERE <condition>;
Example with Condition:
The query below counts the total number of employees whose address is 'Kathmandu'.
Select COUNT(id) from Table WHERE address='Kathmandu';
2. MAX
MAX aggregate function is used to find the Greatest or Highest numerical value in a column.(It doesn't work on string value)
Basic Syntax:
SELECT MAX(column) FROM TABLE
Example:
Following query will find the Maximum Salary from 'tbl_employee' Table.
SELECT MAX(salary) FROM tbl_employee
3. MIN
MIN aggregate function is used to find the Lowest or Smallest numerical value in a column.(It doesn't work on string value)
Basic Syntax:
SELECT MIN(column) FROM TABLE
Example:
Following query will find the Minimum Salary from 'tbl_employee' Table.
SELECT MIN(salary) FROM tbl_employee
4. SUM
SUM aggregate function is used to find the Total Sum of a column.(It doesn't work on string value)
Basic Syntax:
SELECT SUM(column) FROM TABLE;
Example:
Following query will find the Total Salary of All Employeese.
SELECT SUM(salary) FROM tbl_employee;
5. AVG
AVG aggregate function is used to find the Average or Mean value of a column.(It doesn't work on string value)
Basic Syntax:
SELECT AVG(column) FROM TABLE;
Example:
Following Query will find the Average age of the Employees.
SELECT AVG(age) FROM tbl_employee;
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